A typical flip-chip LED has reflective p and n contacts on a bottom surface of the LED, and the contacts are directly connected to bonding pads on a rigid submount that is much larger the LED die. Light generated by the LED is primarily emitted through the top surface of the LED surface. In this way, there are no top contacts that block the light, and wire bonds are not needed.
During fabrication, a submount wafer is populated with an array of LED dies. Electrodes formed on the bottom surface of the LED dies are bonded to pads on the top surface of the submount wafer, and the pads lead to more robust pads on the bottom surface of the submount wafer for bonding to a printed circuit board. The LED dies on the submount wafer are then further processed as a batch on the wafer. Such wafer scale processing may optionally remove the growth substrates from the top surfaces of the LED dies, deposit phosphor over the LED dies, encapsulate the LED dies, and form a lens over each LED. Ultimately, the submount wafer is singulated by, for example, sawing to form separate, packaged LEDs.
Wafer scale processing is efficient. However, the submount wafer or other supporting layer that mechanically supports the thin brittle LED die adds cost. Further, the singulation process for typical supporting layers, such as ceramic or metal, is fairly complex in order to avoid breakage, metal burrs, and other problems.
What is needed is a technique for LED packaging that does not suffer from the above drawbacks.